Restriction-mediated differential display (RMDD) identifies pip92 as a pro-apoptotic gene product induced during focal cerebral ischemia

IER family proteins are regulators of protein phosphatase PP2A and modulate the phosphorylation status of CDC25A

Proteins encoded by immediate-early response (IER) family genes, IER2, IER5, and IER5L, share homology at their N-terminal regions. IER5 binds to protein phosphatase 2A (PP2A) and enhances dephosphorylation of PP2A target proteins such as heat shock factor HSF1. Here, we show the expression of IER family genes and the target protein-specific function of IER proteins. The IER homology regions of IER2 and IER5L are required for the interaction with PP2A. Expression of IER2 and IER5L in cells leads to reduced phosphorylation of HSF1 and derepression of its transcriptional activity. Although IER5 and IER5L enhance dephosphorylation of ribosomal protein S6 kinase, IER2 fails to do so. IER2, IER5, and IER5L all bind to the cell cycle regulator CDC25A and convert it to the hypophosphorylated form, which causes dissociation from 14-3-3 regulatory protein. IER5 differentially regulates CDC25A levels in cells under normal and thermal stress conditions. These results suggest that IER proteins are target protein-specific regulators of PP2A activity and modulate cell proliferation through CDC25A activity.

Cloning and localization of immediate early response 2 (ier2) gene in the brain of medaka

Immediate early response (IER) 2 gene, a member of the IER family, is a gene of unknown function which is affected by external stimuli in the brain. In the present study, the full length sequence and localization of medaka (Oryzias latipes) ier2 was investigated in the brain to understand the functions of Ier2 in the future studies. The full length sequence of medaka ier2 was identified using a 3'-, 5'- rapid amplification of cDNA ends method, and distribution in the brain was identified using in situ hybridization. The identified full length ier2 mRNA consisted of 939 nucleotides spanning along 1 exon. The deduced amino acid sequence consisted of 171 amino acid residues which contains a highly conserved sequence, nuclear localization signal. ier2 mRNA was distributed in the telencephalon, midbrain and the hypothalamus. This highly conserved primary response gene Ier2 can be used to visualize and map functionally activated neuronal circuitry in the brain of medaka.

FGF-dependent left-right asymmetry patterning in zebrafish is mediated by Ier2 and Fibp1

Establishment of left-right asymmetry in vertebrates requires nodal, Wnt-PCP and FGF signaling and involves ciliogenesis in a laterality organ. Effector genes through which FGF signaling affects laterality have not been described. We isolated the zebrafish ier2 and fibp1 genes as FGF target genes and show that their protein products interact. Knock down of these factors interferes with establishment of organ laterality and causes defective cilia formation in Kupffer's Vesicle, the zebrafish laterality organ. Cilia are also lost after suppression of FGF8, but can be rescued by injection of ier2 and fibp1 mRNA. We conclude that Ier2 and Fibp1 mediate FGF signaling in ciliogenesis in Kupffer's Vesicle and in the establishment of laterality in the zebrafish embryo.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

A neuroprotective function for the hematopoietic protein granulocyte-macrophage colony stimulating factor (GM-CSF)

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic cytokine responsible for the proliferation, differentiation, and maturation of cells of the myeloid lineage, which was cloned more than 20 years ago. Here we uncovered a novel function of GM-CSF in the central nervous system (CNS). We identified the GM-CSF alpha-receptor as an upregulated gene in a screen for ischemia-induced genes in the cortex. This receptor is broadly expressed on neurons throughout the brain together with its ligand and induced by ischemic insults. In primary cortical neurons and human neuroblastoma cells, GM-CSF counteracts programmed cell death and induces BCL-2 and BCL-Xl expression in a dose- and time-dependent manner. Of the signaling pathways studied, GM-CSF most prominently induced the PI3K-Akt pathway, and inhibition of Akt strongly decreased antiapoptotic activity. Intravenously given GM-CSF passes the blood-brain barrier, and decreases infarct damage in two different experimental stroke models (middle cerebral artery occlusion (MCAO), and combined common carotid/distal MCA occlusion) concomitant with induction of BCL-Xl expression. Thus, GM-CSF acts as a neuroprotective protein in the CNS. This finding is remarkably reminiscent of the recently discovered functionality of two other hematopoietic factors, erythropoietin and granulocyte colony-stimulating factor in the CNS. The identification of a third hematopoietic factor acting as a neurotrophic factor in the CNS suggests a common principle in the functional evolution of these factors. Clinically, GM-CSF now broadens the repertoire of hematopoietic factors available as novel drug candidates for stroke and neurodegenerative diseases.

NF-kappaB signalling in cerebral ischaemia

In acute stroke, neuronal apoptosis and inflammation are considered to be important mechanisms on the road to tissue loss and neurological deficit. Both apoptosis and inflammation depend on gene transcription. We have identified a signalling pathway that regulates transcription of genes involved in apoptosis and inflammation. In a mouse model of focal cerebral ischaemia, there is an induction of the cytokine TWEAK (tumour necrosis factor-like weak inducer of apoptosis) and its membrane receptor Fn14. TWEAK promotes neuronal cell death and activates the transcription factor NF-kappaB (nuclear factor kappaB) through the upstream kinase IKK [IkappaB (inhibitory kappaB) kinase]. In vivo, IKK is activated in neurons. Neuron-specific deletion of the subunit IKK2 or inhibition of IKK activity reduced the infarct size and neuronal cell loss. A pharmacological inhibitor of IKK also showed neuroprotective properties. IKK-dependent ischaemic brain damage is likely to be mediated by NF-kappaB, because neuron-specific inhibition of NF-kappaB through transgenic expression of the NF-kappaB superrepressor was found to reduce the infarct size. In summary, there is evidence that IKK/NF-kappaB signalling contributes to ischaemic brain damage and may provide suitable drug targets for the treatment of stroke.

JNK- and Rac1-dependent induction of immediate early gene pip92 suppresses neuronal differentiation

The immediate early gene pip92 is rapidly and transiently induced by serum, basic fibroblast growth factor (bFGF), nerve growth factor (NGF) and phobol ester, as well as various toxic stimuli. Rho GTPases, such as RhoA, Rac1 and Cdc42, have been implicated in both cytoskeletal rearrangement and cell cycle control. Rac1 and Cdc42 induce neurite outgrowth in many types of neuronal cells. A downstream effector of both Rac1 and Cdc42, p21-activated kinase (Pak1), is highly enriched in neurons. In the present study, we examined the signal transduction pathways involved in pip92 induction, focusing on the involvement of Rho family guanosine 5'-triphosphate (GTP)ases. We also examined the functional role of pip92 expression during FGF-induced neuronal differentiation in embryonic hippocampal cells. Significant and robust activation of c-Jun N-terminal Kinase (JNK), Rac1 and extracellular signal-regulated kinase (ERK) appeared to be important for pip92 induction in response to bFGF. Transient transfection of kinase-inactive MEKK7 or chemical inhibitors of JNK significantly decreased the activation of Rac1 by FGF. However, blockade of Rac1 did not affect JNK activity. Moreover, a MEK-ERK blockade did not affect Rac1 activity. Activation of JNK and Rac1 induced Pak1 activity, which could then phosphorylate and activate transcription factor Elk1. Stimulation of Pak1-dependent Elk1 was required for the bFGF-induced activation of pip92. Suppression of endogenous pip92 expression by siRNA significantly enhanced bFGF-induced neurite outgrowth, while the ectopic expression of pip92 suppressed the neurite extension. Taken together, these data suggest that neurogenic growth factor-induced expression of pip92 is critical for the regulation of neuronal differentiation, occurring through the subsequent activation of Rac1, JNK, Pak1 and Elk1.

Earliest changes in the left ventricular transcriptome postmyocardial infarction

We report a genome-wide survey of early responses of the mouse heart transcriptome to acute myocardial infarction (AMI). For three regions of the left ventricle (LV), namely, ischemic/infarcted tissue (IF), the surviving LV free wall (FW), and the interventricular septum (IVS), 36,899 transcripts were assayed at six time points from 15 min to 48 h post-AMI in both AMI and sham surgery mice. For each transcript, temporal expression patterns were systematically compared between AMI and sham groups, which identified 515 AMI-responsive genes in IF tissue, 35 in the FW, 7 in the IVS, with three genes induced in all three regions. Using the literature, we assigned functional annotations to all 519 nonredundant AMI-induced genes and present two testable models for central signaling pathways induced early post-AMI. First, the early induction of 15 genes involved in assembly and activation of the activator protein-1 (AP-1) family of transcription factors implicates AP-1 as a dominant regulator of earliest post-ischemic molecular events. Second, dramatic increases in transcripts for arginase 1 (ARG1), the enzymes of polyamine biosynthesis, and protein inhibitor of nitric oxide synthase (NOS) activity indicate that NO production may be regulated, in part, by inhibition of NOS and coordinate depletion of the NOS substrate, L: -arginine. ARG1: was the single-most highly induced transcript in the database (121-fold in IF region) and its induction in heart has not been previously reported.

Long-term gene expression changes in the cortex following cortical ischemia revealed by transcriptional profiling

Cerebral ischemia evokes changes in gene expression time-dependently after the ischemic event. Most studies on transcriptional changes following ischemia have centered on relatively early postischemic time points, and detected multiple genes relevant to neuronal cell death. However, functional outcome after ischemia depends critically on adaptations of the postischemic brain. Plasticity may derive from network-inherent changes, or from the formation of new nerve cells in the CNS. We have screened for gene expression changes up to 3 weeks following a limited photothrombotic cortical insult in the rat sensorimotor cortex by using the sensitive restriction-mediated differential display (RMDD) technique. A high number of genes were detected as induced at early or intermediate time points in the ipsi- and contralateral cortex (6 and 48 h). Unexpectedly, at the late time point examined (3 weeks), we still detected 40 genes that were changed in their expression. We further characterized the expression of two genes linked to neurogenesis (nestin and stathmin), and two genes likely involved in reconfiguring neuronal networks (semaphorin VIa and synaptotagmin IV). Conclusively, our data highlight the degree of long-term transcriptional changes in the cortex after ischemia, and provide insight into functional pathways of relevance for compensatory recovery mechanisms in neural networks.

Tumor necrosis factor-like weak inducer of apoptosis-induced neurodegeneration

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a member of the tumor necrosis factor (TNF) family of cytokines. It has proangiogenic and proinflammatory properties in vivo and induces cell death in tumor cell lines. TWEAK effects are mediated by the membrane receptor Fn14. In a systematic search for genes regulated in a murine stroke model with the tag-sequencing technique massively parallel signature sequencing, we have identified TWEAK as an induced gene. After 24 hr of focal cerebral ischemia in vivo or oxygen glucose deprivation in primary cortical neurons, both TWEAK and its receptor Fn14 were significantly upregulated. TWEAK induced cell death in primary neurons. Transfection of a nuclear factor (NF)-kappaB-luciferase fusion gene demonstrated that TWEAK stimulated transcriptional activity of NF-kappaB through Fn14 and the IkappaB kinase. Inhibition of NF-kappaB reduced TWEAK-stimulated neuronal cell death, suggesting that NF-kappaB mediates TWEAK-induced neurodegeneration at least in part. Intraperitoneal injection of a neutralizing anti-TWEAK antibody significantly reduced the infarct size after 48 hr of permanent cerebral ischemia. In summary, our data show that TWEAK induces neuronal cell death and is involved in neurodegeneration in vivo.

The hematopoietic factor G-CSF is a neuronal ligand that counteracts programmed cell death and drives neurogenesis

G-CSF is a potent hematopoietic factor that enhances survival and drives differentiation of myeloid lineage cells, resulting in the generation of neutrophilic granulocytes. Here, we show that G-CSF passes the intact blood-brain barrier and reduces infarct volume in 2 different rat models of acute stroke. G-CSF displays strong anti-apoptotic activity in mature neurons and activates multiple cell survival pathways. Both G-CSF and its receptor are widely expressed by neurons in the CNS, and their expression is induced by ischemia, which suggests an autocrine protective signaling mechanism. Surprisingly, the G-CSF receptor was also expressed by adult neural stem cells, and G-CSF induced neuronal differentiation in vitro. G-CSF markedly improved long-term behavioral outcome after cortical ischemia, while stimulating neural progenitor response in vivo, providing a link to functional recovery. Thus, G-CSF is an endogenous ligand in the CNS that has a dual activity beneficial both in counteracting acute neuronal degeneration and contributing to long-term plasticity after cerebral ischemia. We therefore propose G-CSF as a potential new drug for stroke and neurodegenerative diseases.

Increased postischemic brain injury in mice deficient in uracil-DNA glycosylase

Uracil-DNA glycosylase (UNG) is involved in base excision repair of aberrant uracil residues in nuclear and mitochondrial DNA. Ung knockout mice generated by gene targeting are viable, fertile, and phenotypically normal and have regular mutation rates. However, when exposed to a nitric oxide donor, Ung(-/-) fibroblasts show an increase in the uracil/cytosine ratio in the genome and augmented cell death. After combined oxygen-glucose deprivation, Ung(-/-) primary cortical neurons have increased vulnerability to cell death, which is associated with early mitochondrial dysfunction. In vivo, UNG expression and activity are low in brains of naive WT mice but increase significantly after reversible middle cerebral artery occlusion and reperfusion. Moreover, major increases in infarct size are observed in Ung(-/-) mice compared with littermate control mice. In conclusion, our results provide compelling evidence that UNG is of major importance for tissue repair after brain ischemia.